Method and apparatus for optical head and optical information reproducing

ABSTRACT

An optical head for reproducing information contained on an optical information disk includes a plurality of light sources and a plurality of light receiving elements in correspondence with the plurality of laser light sources. There is constructed a constitution in which one laser light source in the plurality of laser light sources is constituted by an individual laser diode and which includes a laser module constituted by other laser light sources and the plurality of light receiving elements to thereby enable to realize the small size of the optical head.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S.application Ser. No. 09/644,246, filed Aug. 22, 2000, now U.S. Pat. No.6,714,506 which in turn claims priority from Japanese Patent ApplicationNo. 11-327750, filed on Nov. 18, 1999.

BACKGROUND OF THE INVENTION

The present invention relates to a laser module for processing opticalinformation to record or read information recorded in an opticalrecording medium such as an optical disk or an opto-magnetic disk byusing laser light, and more particularly to a laser module dealing witha plurality of wavelengths such as combination of DVD and CD as well asan optical head and an optical information recording and reproducingapparatus using the same.

In recent years, DVD (Digital Versatile Disc) having a recording densityseven times as much as that of CD, starts spreading rapidly in the formof two wave corresponding drive by which a conventional CD can also beused. In order to maintain compatibility between DVD and CD, the opticalhead used in the drive is provided with laser modules, collimate lensesand object lenses respectively exclusive for CD and DVD, which increasesthe number of parts, complicates optical adjustment and gives rise to anincrease in the cost.

In the meantime, development of blue laser having a wavelength of 410 nmbecomes active and putting to practice thereof in the near future isexpected. Therefore, from now on, it is necessary to conceive an opticalhead in correspondence with three wavelengths which is compatible withCD and DVD and can deal with also blue laser. However, when parts areassembled in correspondence with each of three wavelengths, it isanticipated that reduction in size and thin size formation of theapparatus become difficult and complicated optical adjustment results ina considerable increase in cost.

As a constitution in correspondence with reduction in size of an opticalhead for multiple wavelengths and promotion of reliability thereof, forexample, in Japanese Patent Laid-Open No. Hei 10-21577, there isdisclosed an example in which two or three semiconductor laser chips arepasted on a silicon substrate having a micromirror and light receivingelements to thereby constitute a module.

However, in the case in which two semiconductor laser chips arearranged, when one of the chips is aligned to an optical axis, the otherof the chips becomes out of the optical axis and therefore, it isnecessary to provide means for correcting chromatic aberration. Further,in the case in which three laser chips are integrated to a siliconsubstrate having light receiving elements, it is necessary to correctchromatic aberration of two pieces of laser light out of the opticalaxis. However, a burden on a polarizing diffraction grating or a focuslens becomes considerable and it is difficult to use the constitutioninto practice as the optical head. Further, an area of the siliconsubstrate having the three laser chips and the light receiving elementsin correspondence with respective light sources, becomes large-sized,resulting in hindrance for reduction in size and price of the lasermodule.

For example, there is shown a silicon substrate arranged with threelaser chips having a chip width of 0.25 mm in FIG. 4. A width of arecess portion (hereinafter, referred to as sink portion) on thesubstrate arranged with the chips becomes as large as 1.1 mm. Further,when light receiving elements for focusing and for tracking incorrespondence with respective laser light are arranged on oppositesides of the sink portion, the width of the silicon substrate becomes aslarge as about 3.9 mm and the number of silicon substrates taken from asilicon wafer decreases and the constitution becomes expensive. In themeantime, it is extremely difficult to bond three laser chips in onesilicon substrate proximately to each other since a material of a deviceof semiconductor laser having a wavelength of 410 nm is GaN and amaterial of a device of DVD or CD laser is GaAs which is different fromGaN.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided anoptical head including a plurality of laser light sources and aplurality of light receiving elements in correspondence with theplurality of laser light sources, said optical head comprising: onelaser light source of the plurality of laser light sources, formed as anindividual laser diode; and a laser module comprising laser lightsources other than the one laser light source of the plurality of laserlight sources and the plurality of light receiving elements; whereinlaser light emitted from the plurality of laser light sources is made topass through a beam splitter and is guided to an optical informationmedium, and the reflected light from the optical information medium isguided to the laser module by the beam splitter.

According to another aspect of the present invention, there is providedthe optical head according to the above-described aspect wherein thelaser module includes two wave laser light sources, an optical axis ofthe laser light of the laser module is aligned with that of the laserlight of the laser diode by the beam splitter, the laser light iscollimated into parallel light by a collimator lens and then focused onthe optical information medium by a focus lens, and the reflected laserlight is guided to the light receiving elements in the laser module viaa polarizing diffraction grating and the beam splitter.

Further, according to another aspect of the present invention, there isprovided the optical head according to the above-described aspectwherein the laser module includes one wave laser light source.

Further, according to another aspect of the present invention, there isprovided the optical head according to the above-described aspectwherein a beam shaping prism is arranged between the laser diode and thebeam splitter.

Further, according to another aspect of the present invention, there isprovided an optical head including a plurality of laser light sourcesand a plurality of light receiving elements in correspondence with theplurality of laser light sources, said optical head comprising: a lasermodule in which at least one laser light source of the plurality oflaser light sources is pasted on a substrate having the plurality oflight receiving elements as a laser chip; and laser light sources otherthan said at least one laser light source of the plurality of laserlight sources, formed as individual laser diodes; wherein laser lightemitted from the plurality of laser light sources is made to passthrough a beam splitter and is guided to an optical information medium,and the reflected light from the optical information medium is guided tothe light receiving elements in the laser module by the beam splitter.

Further, according to another aspect of the present invention, there isprovided the optical head according to the above-described aspectwherein the laser diodes include two wave laser light sources, the lasermodule includes one wave laser light source, an optical axis of thelaser light of one of the laser diodes is aligned with that of the laserlight of the laser module by the beam splitter, the laser light iscollimated into parallel light by a collimator lens and then focused onthe optical information medium by a focus lens, and the reflected laserlight is converted into primary diffraction light by a polarizingdiffraction grating to be guided to the light receiving elements incorrespondence with three laser light sources in the laser module viathe beam splitter.

Further, according to another aspect of the present invention, there isprovided an optical information recording and reproducing apparatuscomprising: the optical head according to any one of Claims 1 through 6;optical information medium determining means; and light source selectingmeans; wherein laser light sources are selected by the light sourceselecting means in accordance with a result of determination of theoptical information medium determining means.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects, advantages and novel features of the present invention willbecome apparent from the following description of the inventionpresented in conjunction with the accompanying drawings, wherein:

FIG. 1 is a view showing a constitution of an optical head having threewavelengths light sources according to the present invention,illustrating the optical path for DVD and CD formatted optical disks;

FIG. 2 illustrates the optical path of the constitution shown in FIG. 1for a high density DVD formatted optical disk;

FIG. 3 is a view showing an embodiment of a laser module in FIGS. 1 and2;

FIG. 4 is a view showing an of a laser module when three wavelengthlight sources are aligned;

FIG. 5 is a view showing a constitution of an optical head having twowavelength light sources according to the present invention;

FIG. 6 is a view showing the constitution of the optical head having thetwo wavelength light sources according to the present invention; and

FIG. 7 is a view showing an embodiment of a laser module in FIGS. 5 and6.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIGS. 1 and 2 show a first constitution of an embodiment of an opticalhead according to the present invention, in which FIG. 1 shows anoptical path during reproducing or recording and reproducing DVD-ROM,RAM (wavelength of 650 nm) or CD, CD-R (wavelength of 780 nm) and FIG. 2shows an optical path during reproducing or recording and reproducinghigh density DVD (wavelength of 410 nm).

In FIG. 1, when the optical head is used for DVD-ROM, RAM, laser lightemitted from a semiconductor laser chip 11 having a wavelength of 650 nmin a laser module 1 is reflected by a beam splitter 3, the reflectedlight is collimated into parallel rays by a collimator lens 4, and isfocused on a record face of an optical disk 8 having a thickness of 0.6mm of DVD by a focus lens 6.

When the optical head is used for CD, CD-R, laser light emitted from asemiconductor laser chip 12 having a wavelength of 780 nm in the lasermodule 1 is reflected by the beam splitter 3, the reflected light iscollimated into parallel rays by the collimator lens 4, and is focusedon an optical disk 9 having a thickness of 1.2 mm of CD by the focuslens 6.

In this case, correction of a focus position owing to a differencebetween plate thicknesses of DVD and CD is carried out by the focus lensand when light is converged to the optical disk 8 having a thickness of0.6 mm of DVD, the correction is constituted to minimize primary sidelobe and with regard to the optical disk 9 having a thickness of 1.2 mmof CD-R, the correction is carried out such that only inner peripherallight is used.

In the meantime, correction of chromatic aberration caused since thelaser chip 12 of 780 nm is arranged out of an optical axis is made tocope with by the aspherical shape of the focus lens 6. Reflected lightfrom the optical disk 8 or 9 passes through the focus lens 6 to beformed into primary diffracted light by the polarizing diffractiongrating 5. The primary diffracted light formed falls on the collimatorlens 4, is reflected by the beam splitter 3 and thereafter enters alight receiving element substrate 15 in the laser module 1 as can beseen in FIG. 3. Further, reflected light from the optical disk 8 or 9 isconverted into an electric signal and is outputted in the respectivelight receiving elements.

FIG. 2 shows an optical path of high density DVD (having a wavelength of410 nm). In the case of a laser diode 2, laser light emitted from asemiconductor laser chip 13 having a wavelength of 410 nm passes throughthe beam splitter 3, collimated into parallel rays by the collimatorlens 4 and is focused on an optical disk 10 for high density DVD by aspecific focus lens 7. Further, reflected light from the optical disk 10passes through the focus lens 7 to be formed into the primary diffractedlight 14 by the polarizing diffraction grating 5. The primary diffractedlight 14 falls on the collimator lens 4, reflected by the beam splitter3 and thereafter enters the light receiving elements on the lightreceiving element substrate 15 provided in the laser module 1 to beconverted into an electric signal and then to be outputted.

FIG. 3 shows an embodiment of the light receiving element substrate 15mounted with the laser chips 11 and 12. According to the light receivingelement substrate, the focusing error and the tracking error aredetected independently from each other for three wavelengths of 410 nm,650 nm and 780 nm. In this case, focusing operation is carried out bythe Knife Edge method and the tracking operation is carried out by theDifferential Phase Detection method.

On the left side of the laser chip portion of the light receivingelement substrate 15, there are arranged light receiving elements fortracking and for detecting a signal, having constitutions of 16(a),17(a) and 18(a) for wavelengths of 410 nm, 650 nm and 780 nm, while onthe right side of the laser chip portion of the light receiving elementsubstrate 15, there are arranged light receiving elements for detectingfocus, having constitutions of 16(b), 17(b) and 18(b) for wavelengths of410 nm, 650 nm and 780 nm. The laser chip 11 having a wavelength of 650nm and the laser chip 12 having a wavelength of 780 nm adopt a junctiondown structure in which emitting portions thereof are disposed at lowerpositions to ensure heat radiation. The laser chips 11 and 12 are bondedon a recess portion (sink portion) of the light receiving elementsubstrate 15. Further, there is constituted a structure in which emittedlight from the respective laser is reflected by a micromirror 19utilizing an inclined face of the recess portion and the reflected lightvertically rises from the light receiving element substrate 15. A risepoint of the laser light on the micromirror 19 is referred to as an“apparent light emitting point”.

When a distance from an apparent light emitting point 20 of laser lighthaving a wavelength of 650 nm to the light receiving element portion17(a) for detecting focus of laser light having a wavelength of 650 nmor to the light receiving element 17(b) for tracking and detecting asignal, is designated by notation R650 and a distance from an apparentlight emitting point 21 of laser light having a wavelength of 780 nm tothe light receiving element portion 18(a) for detecting focus having awavelength of 780 nm or to the light receiving element 18(b) fortracking and detecting a signal, is designated by notation R780, arelationship (1) is expressed in association with a pitch “p” of thepolarizing diffraction grating 5, a laser wavelength “λ” and a focallength F_(c) of the collimator lens 4: $\begin{matrix}{{R = \frac{F_{c}\bullet\quad\lambda}{p}},\quad{where}} & (1)\end{matrix}$

-   -   F_(c) is the focal length of the collimator lens;    -   λ is the semiconductor laser wavelength; and    -   p is the polarizing diffraction grating pitch.

According to the embodiment, R=929 μm when Fc=20 mm, p=14 μm and thewavelength is 650 nm and R=1114 μm when the wavelength is 780 nm. Thelight emitting point of the laser light having a wavelength of 410 nmcoincides with the light emitting point 20 of the laser light having awavelength of 650 nm, the distance R=586 μm and the width of the lightreceiving element substrate 15 falls in a range equal to or smaller than2.5 mm.

FIG. 4 shows a prior art constitution of a light receiving elementsubstrate where three laser chips are arranged in order to compare thesize of the light receiving element substrate 15 therewith. A width ofthe light receiving element substrate 22 needs 3.9 mm, an area of thelight receiving element substrate is increased by 50% or more and thenumber of the elements taken from a wafer is considerably reduced, whichgives rise to an increase in cost. Further, two pieces of the laserlight of the laser chip 11 having a wavelength of 780 nm and the laserchip 13 having a wavelength of 410 nm are arranged out of the opticalaxis and correction of chromatic aberration is needed. However, afterall, the correction cannot be made to cope with only by the asphericalshape of the focus lens. Further, in consideration of a technicaldifficulty of arranging and bonding three chips with high accuracy andsevereness of yield with regard to function after mounting therespective semiconductor laser chips on the silicon substrate,advantages in view of the cost provided by the embodiment are enormous.

Although according to the above-described constitution shown in FIG. 3,the laser module 1 is mounted with two of the semiconductor laser chipshaving a wavelength of 780 mm and a wavelength of 650 nm, when the laserchips having a wavelength of 780 nm and a wavelength of 650 nm areincorporated in a single semiconductor laser chip, fabrication of thelaser chip to the silicon substrate is facilitated and further merit inview of the cost is achieved.

In the meantime, it is possible that the laser diode 2 is mounted withtwo semiconductor laser chips having a wavelength of 780 nm and awavelength of 650 nm (shown in FIG. 1 by phantom lines as 2′) or mountedwith the above-described two wave semiconductor laser chip (shown inFIG. 1 by phantom lines as 2″), and the laser module 1 is mounted withthe laser chip having a wavelength of 410 nm (shown in FIG. 1 by phantomlines as 1′).

Further, a whole optical information recording apparatus has determiningmeans for CD, DVD, and high density DVD disk, laser having wavelengthsof 780 nm, 650 nm or 410 nm is selected by using laser light sourceselecting means in accordance with a result of the determination, and anoptimum light source is made to emit light to thereby carry outinformation recording.

Next, FIGS. 5 and 6 show a second constitution of an embodiment of anoptical head according to the present invention, showing an embodimentpreferable for utilizing efficiently power of the laser chip in dealingwith two wavelengths accompanied by CD-R recording such as DVD-ROM andCD-R or DVD-RAM and CD-R.

In the case of using the optical head for DVD-ROM or RAM, as shown inFIG. 5, laser light emitted from a semiconductor laser chip 11 having awavelength of 650 nm in a laser module 23 is reflected by a beamsplitter 26, the reflected light is collimated into parallel rays by acollimator lens 4 and is focused on the record face of an optical disk 8having a thickness of 0.6 mm of DVD by a focus lens 27. In the meantime,in the case of using the optical head for CD-R, as shown in FIG. 6,laser beam emitted from a semiconductor laser chip 25 having awavelength of 780 nm for CD-R of a laser diode 24 passes through thebeam splitter 26, is collimated into parallel rays by the collimatorlens 4 and is focused on an optical disk 9 having a thickness of 1.2 mmof CD by the focus lens 27. As described above, the correction of thefocus position owing to the difference between the plate thicknesses ofDVD and CD is made to cope with by the aspherical shape of the focuslens 27. However, CD-R is designed to use only the inner peripherallight and therefore, it is difficult to ensure an optical amountsufficient for recording by CD-R at the optical disk 9. Therefore, asmeans for providing the optical amount sufficient for CD-R recording, abeam shaping prism 28 is arranged between the laser diode 24 and thebeam splitter 26 and the efficiency of utilizing the laser light ispromoted by constituting the laser light of CD-R in a circular shape.For example, there is corrected light flux in an elliptical shape ofabout 10° or 30° in full width half maximum emitted from thesemiconductor laser. According to the method, in comparison with amethod of constituting an optical output of CD-R laser diode 16 withhigh power, the condition for use in high temperature is alleviated,promotion of the reliability is achieved and factors of increasing thecost such as a deterioration in function and yield of laser owing to thehigh powered structure or adoption of a heat sink excellent in thermalconductivity, can be restrained.

Continuing with FIG. 6, reflected light from the optical disk 8 or 9passes through the focus lens 27, falls on a polarizing diffractiongrating 29 to be formed into primary diffracted light. Then the primarydiffracted light falls on the collimator lens 4, reflected by the beamsplitter 26 and thereafter enters a light receiving element substrate 30provided in a laser module 23. Further, the reflected light is convertedinto an electric signal and is outputted at each light receiving portionof a light receiving element.

FIG. 7 shows an embodiment of the light receiving element substrate 30mounted with the laser chip 11. The focal length of the collimator lensis 20 mm, the polarizing diffraction grating pitch is 20 μm. From theabove-described Equation (1), when a wavelength of 650 nm, R=660 μm,when a wavelength of 780 nm, R=780 μm, a width of the silicon substrate30 falls in a range equal to or smaller than 1.0 mm. Therefore the areaof the substrate can be restrained to a half or smaller of that in thecase of mounting two laser chips and the cost can be reduced.

Further, although according to the embodiment, an explanation has beengiven by taking an example of a wavelength of 650 nm for DVD-ROM, RAM, awavelength of 780 nm for CD, CD-R and a wavelength of 410 nm for highdensity DVD, the embodiment is not limited to wavelengths of 650 nm, 780nm and 410 nm. For example, it is apparent that the embodiment isapplicable for numerical values of 650±10 nm, 780 nm±10 nm, 400±10 nm.As explained in details, according to the embodiment, in the opticalhead for recording or reproducing optical information recording mediahaving two different wavelengths, there is provided the optical headrealizing simplification of fabricating the apparatus, manufacturingindividual parts with low cost, strong at a change in temperature andpromoting the reliability by reducing the number of parts, and theembodiment contributes to miniaturization and reduction in cost of theoptical head for recording or reproducing the optical informationrecording medium having three different wavelengths.

1. An optical head for focusing laser light on an optical informationmedium and receiving reflected light from the optical information mediumcomprising: a first laser emitting component disposed on a firstsubstrate and operable to produce laser light at a first wavelength; anda second laser emitting component disposed on a second substrate andoperable to produce laser light at a second wavelength and to detectlaser light, the second substrate separate from the first substrate, thesecond laser emitting component comprising: a first light receivingelement disposed on the second substrate and arranged to receivereflected light of the laser light of the first wavelength; and a secondlight receiving element disposed on the second substrate and arranged toreceive reflected light of the laser light of the second wavelength,wherein the first laser emitting component is further configured toproduce laser light of a third wavelength different from the firstwavelength and different from the second wavelength, wherein the secondlaser emitting component further comprises a third receiving elementdisposed on the second substrate to receive reflected light of the laserlight of the third wavelength.
 2. The optical head of claim 1 whereinthe first wavelength is different from the second wavelength.
 3. Theoptical head of claim 1 wherein the second wavelength is about 410nanometers.
 4. The optical head of claim 3 wherein the first wavelengthis about 650 nanometers and the third wavelength is about 780nanometers.
 5. An optical head for focusing laser light on an opticalinformation medium and receiving reflected light from the opticalinformation medium comprising: a first laser emitting component disposedon a first substrate and operable to produce laser light at a firstwavelength; and a second laser emitting component disposed on a secondsubstrate and operable to produce laser light at a second wavelength andto detect laser light, the second substrate separate from the firstsubstrate, the second laser emitting component comprising: a first lightreceiving element disposed on the second substrate and arranged toreceive reflected light of the laser light of the first wavelength; anda second light receiving element disposed on the second substrate andarranged to receive reflected light of the laser light of the secondwavelength, wherein the second laser emitting component is furtherconfigured to produce laser light of a third wavelength different fromthe first wavelength and different from the second wavelength, andwherein the second laser emitting component further comprises a thirdreceiving element disposed on the second substrate to receive reflectedlight of the laser light of the third wavelength.
 6. An optical head fordirecting laser light to an optical information medium and for receivingreflected laser light from the optical information medium, comprising: alaser chip for emitting a first beam of light at a first wavelength, thelaser diode disposed on a first substrate; a laser module comprising asecond substrate separate from the first substrate, the laser module foremitting at least second beam of light at a second wavelength, the lasermodule further having a plurality of receiving elements disposed on thesecond substrate; a beam splitter to guide the first and the secondbeams to the optical information medium; and a focus lens to focus thefirst and second beams onto the optical information medium, therebyproducing reflected light from the optical information medium, the beamsplitter guiding the reflected light to the receiving elements of thelaser module, wherein the laser chip is configured to selectivelyproduce the first beam of light at the first wavelength and at a thirdwavelength, wherein the beam splitter is disposed such that an opticalaxis of the first beam of light is substantially in alignment with anoptical axis of the second beam of light.
 7. An optical head fordirecting laser light to an optical information medium and for receivingreflected laser light from the optical information medium, comprising: alaser chip for emitting a first beam of light at a first wavelength, thelaser diode disposed on a first substrate; a laser module comprising asecond substrate separate from the first substrate, the laser module foremitting at least second beam of light at a second wavelength, the lasermodule further having a plurality of receiving elements disposed on thesecond substrate; a beam splitter to guide the first and the secondbeams to the optical information medium; and a focus lens to focus thefirst and second beams onto the optical information medium, therebyproducing reflected light from the optical information medium, the beamsplitter guiding the reflected light to the receiving elements of thelaser module, wherein the laser module is configured to selectivelyproduce the second beam light at the second wavelength and at a thirdwavelength, wherein the beam splitter is disposed at a location suchthat an optical axis of the first beam of light is substantially alignedwith an optical axis of the second beam of light.
 8. The optical head ofclaim 7 wherein the laser module comprises a first laser chip and asecond laser chip disposed on the second substrate.
 9. The optical headof claim 8 wherein the laser chip is configured to produce the firstbeam of light at only the first wavelength.
 10. The optical head ofclaim 6 further comprising a beam shaping prism disposed between thelaser diode and the beam splitter.
 11. The optical head of claim 5wherein the first wavelength is different from the second wavelength.12. The optical head of claim 5 wherein the second wavelength is about410 nanometers.
 13. The optical head of claim 5 wherein the firstwavelength is about 650 nanometers and the third wavelength is about 780nanometers.